Screw cap



FIG. 1 is a side view of a screw cap, showing my design;

FIG. 2 is a top view thereof;

FIG. 3 is a bottom view thereof;

FIG. 4 is a top perspective view thereof; and,

FIG. 5 is a bottom perspective view thereof.

The broken lines shown in the drawings illustrate portions of the screw cap and form no part of the claimed design. 

CLAIM The ornamental design for a screw cap, as shown and described. 